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Car shudders when you accelerate on gas 

 

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 Post subject: Car shudders when you accelerate on gas
Posted: Wed Nov 14, 2012 11:17 am 
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I have a BA Fairmont on direct injected gas (also on petrol) and whenever I accelerate at least 1/2 throttle the car will shudder a bit, doesn't do it any other time. It runs fine on petrol though.

Was thinking about getting the gas system looked at but wanted to find out if there was an easy fix on here first.

What causes gas systems to shudder on acceleration? Cheers.

Last edited by Tech90 on Thu Nov 15, 2012 5:37 pm, edited 1 time in total.

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 Post subject: Re: Car shutters when you accelerate on gas
Posted: Wed Nov 14, 2012 5:00 pm 
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how many KM has it done since the last time it had the plugs and coils changed?

 

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 Post subject: Re: Car shutters when you accelerate on gas
Posted: Wed Nov 14, 2012 5:04 pm 
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tickford_6 wrote:
how many KM has it done since the last time it had the plugs and coils changed?

Not sure, haven't had the car for long. I bought plugs for it today to suit dual fuel. I'll soon find out if it's gapped right...
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 Post subject: Re: Car shutters when you accelerate on gas
Posted: Wed Nov 14, 2012 6:09 pm 
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not being a smart@ss, but the word is `shudders'

 

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 Post subject: Re: Car shutters when you accelerate on gas
Posted: Wed Nov 14, 2012 6:20 pm 
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tearlejc wrote:
not being a smart@ss, but the word is `shudders'

All good, same same anyway!
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 Post subject: Re: Car shutters when you accelerate on gas
Posted: Thu Nov 15, 2012 10:30 am 
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Tech90 wrote:
tickford_6 wrote:
how many KM has it done since the last time it had the plugs and coils changed?

Not sure, haven't had the car for long. I bought plugs for it today to suit dual fuel. I'll soon find out if it's gapped right...




Use a 0.9mm gap with LPG, You'll extend the life of the coils.

 

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 Post subject: Re: Car shutters when you accelerate on gas
Posted: Thu Nov 15, 2012 5:36 pm 
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Okay thanks. If it's the coils, are they easy to replace?
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 Post subject: Re: Car shudders when you accelerate on gas
Posted: Fri Nov 16, 2012 2:49 am 
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Injected LPG = 1.1mm spark plug electrode gap.

Misfiring on acceleration = ignition problem - plugs & coils. When replacing these, make sure you generously apply dielectric grease on the rubber boots of each coil (inside and out).

 

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 Post subject: Re: Car shudders when you accelerate on gas
Posted: Fri Nov 16, 2012 9:31 am 
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PoweredByCNG wrote:
Injected LPG = 1.1mm spark plug electrode gap.

Misfiring on acceleration = ignition problem - plugs & coils. When replacing these, make sure you generously apply dielectric grease on the rubber boots of each coil (inside and out).

Okay thanks for the advice.

Would these work fine for a car on dual fuel? http://www.ebay.com.au/itm/Ford-BA-BF-F ... 3cc7b9a6bc

And this grease I should be able to get from supercheap/other car parts store?

Cheers
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 Post subject: Re: Car shudders when you accelerate on gas
Posted: Fri Nov 16, 2012 4:40 pm 
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The factory 1.1mm gap and service interval causes premature failure of the coils.

0.9 gap and change at 80 000km and you will greatly prolong the life of the coils and will not cause any loss of power or economy.

 

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 Post subject: Re: Car shudders when you accelerate on gas
Posted: Fri Nov 16, 2012 4:46 pm 
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tickford_6 wrote:
The factory 1.1mm gap and service interval causes premature failure of the coils.


Factory plugs for a petrol-only engine is 1.3-1.5mm. 1.1mm for LPG is perfectly fine considering that the original E-gas spec was 1.1mm (before they revised it to 0.7-0.9mm). The only reason to close the gap is to reduce risk of backfire and such risks are already eliminated with an injected LPG system. Too narrow a gap also adversely affects engine operation on petrol.

Quote:
0.9 gap and change at 80 000km and you will greatly prolong the life of the coils and will not cause any loss of power or economy.


1.1mm gap with Bosch FR 7 KPP 33U+ double platinum spark plugs will last you close as makes no difference to 100,000km, and will furthermore place less stress on the rest of your ignition components as they wear (compared to iridium). Iridium plugs in my experience don't last on LPG.

 

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 Post subject: Re: Car shudders when you accelerate on gas
Posted: Fri Nov 16, 2012 4:53 pm 
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Quote:
1.1mm gap with Bosch FR 7 KPP 33U+ double platinum spark plugs will last you close as makes no difference to 100,000km, and will furthermore place less stress on the rest of your ignition components as they wear (compared to iridium). Iridium plugs in my experience don't last on LPG.

What gap size are these plugs? Cause theyre the ones I bought to replace my current ones.
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 Post subject: Re: Car shudders when you accelerate on gas
Posted: Fri Nov 16, 2012 7:42 pm 
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Tech90 wrote:
What gap size are these plugs? Cause theyre the ones I bought to replace my current ones.


They should be 1.1mm but check with a feeler gauage.

 

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 Post subject: Re: Car shudders when you accelerate on gas
Posted: Sat Nov 17, 2012 3:25 am 
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Checked the part number of the plugs again and I got it slightly wrong before. The actual part number is:

FR 7 KPP 33U-P-P6

You will want to re-gap the plugs to 1.1mm for an injected LPG application as these plugs are set to 0.9mm as standard.

 

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 Post subject: Re: Car shudders when you accelerate on gas
Posted: Sun Nov 18, 2012 9:19 pm 
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PoweredByCNG wrote:
Factory plugs for a petrol-only engine is 1.3-1.5mm. 1.1mm for LPG is perfectly fine considering that the original E-gas spec was 1.1mm (before they revised it to 0.7-0.9mm). The only reason to close the gap is to reduce risk of backfire and such risks are already eliminated with an injected LPG system. Too narrow a gap also adversely affects engine operation on petrol.




Like I said, the factory gap of 1.1mm along with factory change interval causes premature failure of the coils. As the plugs wear the gap opens and the energy needed to spark across the gap increases and it puts undue stress on the coils. If you close the gap to a perfectly reasonable 0.9mm and drop the change interval back to 80 000km you will extend the life of the coils.

Ford revised it back because the plugs were wearing so much over the 'life' of the plugs that the cars were back firing and coils were failing under warranty. Sure the injection stops the back firing (it just becomes a misfire instead), but it doesn't stop the added stress on the coils. If you want to keep the 1.1mm gap, then change them every 40 000km if you want the coils to live.

 

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